Method of preparing metal oxide-metal sulfide plural coated siliceous fibers



Unite Patented Mar. 5, 1968 3,372,051 METHOD F PREPARHNG METAL OXIDE-METAL SULFIDE PLURAL COATED SILKCEOUS FIBERS Charles .l. Stalego, Newark, Ohio, assignor to Owens- Corning Fiberglas Corporation, a corporation of Delaware No Drawing. Filied Get. 28, 1963, Ser. No. 319,552 10 Claims. cs. 117-69) ABSTRACT OF THE DISCLQSURE Siliceous fibers are provided with a porous metal base coating consisting of the oxides of chromium, zirconium, aluminum, titanium, cobalt and/or iron, formed by the hydrolysis and subsequent thermal dehydration of from 525% by weight of the combined weight of substrate and coating, of a water soluble metal salt wherein the base coating is subsequently impregnated witha different water soluble metal salt, or combination of salts, reacted with a sulfide yielding compound to form, in situ, the sulfides of these different metals consisting of barium, silver, lead, cadmium, lithium and/or zinc. High temperature and abrasion resistant siliceous fibers are disclosed for use in high temperature applications, wherein said lubricious coating, as it is worn away, replenished from its reservoir in the porous metal base coating.

The present invention relates to treatments for siliceous fibers and to the temperature and abrasion resistant fibers prepared by such treatments, and particularly to siliceous fibers provided with a metal base coating which is impregnated with a dry lubricant which also comprises a metal compound.

The inert nature, high strengths and thermal resistance of siliceous fibers such as glass, mineral wool and silica fibers, have long rendered them desirable in applications involving exposure to high temperatures. However, their utility in such applications has been limited by the detrimental charcateristic of mutual abrasion which is inherent in such fibers. Specifically, while siliceous fibers are usable in high temperature applications attended by static conditions, such utility cannot be extended to dynamic environments in which the fibers rub against one another and' rapidly degrade the fibrous structure.

To overcome this drawback, protective coatings such as polytetrafiuoroethylene and silicone resins have been utilized upon siliceous fibers employed in high temperature applications. While such coatings provide a protective sheath about the fibers and impart lubricity to overcome abrasion inspired attrition, they are somewhat limited in respect to thermal resistance. In essence, there is still a gap between the temperature resistance of such coatings and that of the siliceous fibers, which consequently limits the utility of the fibers to the lower resistance of the specified coatings materials, e.g. approximately 500 F.

It is an object of the present invention to provide coated siliceous fibers having increased thermal and abrasion resistance.

Another object is the provision of methods for the preparation of siliceous fibers having increased thermal and abrasion resistance.

A further object is the provision of coatings of improved thermal and abrasion resistance.

The foregoing objects are achieved by means of the application of a plural phase coating to the surfaces of siliceous fibers, or to substrates formed from siliceous fibers, e.g. fabrics, yarns, random mats, etc. While the inventive coating consists of two principal phases, i.e. a relatively porous metal base coating and a lubricious metal impregnant applied to the base coating, it should be noted that each of the two principal phases may comprise a plurality of compositions as will be subsequently explained.

More specifically, the base coating predominantly comprises one or more metal oxides, while the subsequent lubricious impregnant consists principally of one or more metal sulfides.

While the base coating has been described as porous for the purpose of expressing its ability to retain the subsequently applied lubricious impregnant, it might more properly be referred'to as possessed of a roughened or ciscontinuous surface. Electron photomicrographs have shown the surface of the base coating to possess an appearance like that of crudely chipped flint or weathered slate.

The presence of compositions other than metal oxides in the base coating, is the consequence of the desirability for achieving the in situ formation of the metal oxide coating, due to the difficulty of directly applying such a coating. While a metal oxide coating may be achieved through a sintering technique or through the entrainment of the oxide in a carrier phase, such methods are difficult, yield coatings of limited durability, and may entail damage to the substrate. Accordingly, the base coatings of the invention are preferably derived through the application of a metal compound other than an oxide which is subsequently converted or transformed to the corresponding metal oxide. As the result of such conversion, the base coating may contain a significant portion of compositions other than the oxide, e.g. the by-products of the conversion to the metal oxide.

In a preferred method for the formation of the base coating of metal oxide, a soluble metal salt is first applied to the substrate and then converted to the corresponding metal hydroxide .or hydrous metal oxide, e.g. through reaction with ammonia fumes. The hydroxide or hydrous oxide is then converted to the corresponding metal oxide by means of thermal transformation .or chemical reaction.

Alternatively, a soluble metal hydroxide may be applied to the substrate and converted to the corresponding metal oxide. Still further, a metal salt may be applied to the substrate and directly convered to the oxide without the necessity for an intermediate conversion to the corresponding hydroxide. For example, sodium dichromate may be reacted with sulfur to yield chromic oxide and sodium sulfate, with the latter removed by washing if desired. However, as will be later demonstrated, a thermal treatment of such a coating is still desirable.

The second coating or impregnant which is applied to the metal oxide base coating is a metal sulfide which is capable of imparting lubricity to the treated structure. While soluble metal sulfides, e.g. barium trisulfide or tetrasulfide, may be applied directly to the substrate, a preferred technique involves the application of a soluble metal salt, e.g. barium nitrate, and its conversion to the corresponding metal sulfide by means of reaction with sulfur yielding compounds, e.g. hydrogen sulfide. Such a method may also entail the deposition of materials other than the metal sulfide, or reaction by-products, in the secondary or impregnating coating, e.g., barium sulfate and residual barium nitrate in the case of the in situ conversion of barium nitrate to barium sulfide.

The previously described methods for the attainment of the plural phase inventive coating are graphically demonstrated by the fOllOWiHg flow chart:

the corresponding metal hydroxide or hydrous oxide, and ultimately transformed into the corresponding metal oxide. The base coating may be applied by conventional means, e.g. immersion, spraying, contact applicators, etc., and it has been found desirable to apply between 5 to by weight of the metal compound, and preferably between 8 to 13% by weight (based upon the combined weight of the substrate and coating). In this regard, it has been found that a base coating of less than 5% by weight tends to yield a relatively negligible improvement in product properties while the use of more than 25% by Weight renders the subsequent impregnation of the base coating difiicult of achievement while simultaneously reducing the flexibility of the coated structure. Consequently, the concentration of the treating solution employed, the dura- SOLUBLE METAL SALT APPLIED TO SUBSTRATE SOLUBLE METAL HYDROXIDE APPLIED -TO SUBSTRATE SOLUBLE FETAL SALT APPLIED TOSUBS'I'RATE comm: T0 CORRESPONDING METAL maoxmn IHEIMAL PRANSFORMATION TO CORRESPONDING METAL OXIDE IMPREGNATION BY- METAL SALT CONVERSION OF METAL SALT TO CORRESPONDING I'TETAL SULFIDE SILICKDUS SUBTRA'IE PROVIDED WITH METAL OXIDE BASE COAT- ING: AND METAL SULFIUE IBERI- OIUUS IMPREHNANT As a consequence of the foregoing treatment, the siliceous fibers, or substrates formed from siliceous fibers, are provided with a metal oxide base coating characterized by excellent thermal resistance, and a lubricious surface impregnant capable of providing an abrasion resistant lubricity during exposure to both ambient and elevated temperatures.

As previously stated, the base coating is preferably ap- DIRECTLY CONVERTED T0 CORRESPONDING- METAL OXIDE IHPREGNATION BY. SOLUBLE METAL SULFIDE tion and degree of the coating application, and the nature of the substrate, should be calculated to yield a coating of between 5 to 25% by weight. For example, a tightly wound bolt of glass fabric might require prolonged exposure to the coating medium and/or a pressurized or vacuum coating technique while an open fibrous mat could be merely immersed for a short period. Vacuum or pressurized coating techniques may also be employed in plied as a soluble metal salt which is then converted to the other. coating or impregnation methods of the invention, e.g. impregnation with the metal salt which is subsequently converted to the corresponding metal sulfide.

The conversion of the metal salt to the corresponding metal hydroxide or hydrous oxide may be simply achieved by means of a short exposure of the substrate coated with the metal salt to a suitable reactant, e.g. ammonia fumes. In the case of the direct conversion of the salt to the corresponding metal oxide more elaborate procedures may be required. For example, while a chromic oxide coating may be formed through the heating of an admixture of sulfur and sodium dichromate with an optional removal of the resultant sodium sulfate by means of washing, other methods may entail controlled environments and additional treating materials, e.g. perchlorates, etc.

In addition, the conversion of the metal hydroxide or hydrous oxide to the correspondingmetal oxide may be realized with simple means and conventional heating apparatus or ovens. While a heat treatment in the range of 500-900 F. for a period of from a few minutes to 6 hours is preferred, the extent and condition of the treatment is naturally dependent upon the thermal conditions required for the oxidation of the specific metal hydroxide, and the thermal resistance of the substrate. For example, hydrous chromic oxide may be adequately, but not entirely, converted to chromic oxide by heating at 600 F. for a period of one hour. However, complete conversion, or the conversion of other metal hydroxides, may entail more rigorous and/or prolonged treatments. In addition, the susceptibility of the substrate to thermal degradation may require lower temperatures or the curtailment of the heatin phase. For example, conventional boro-silicate glass tends to soften at temperatures in the range of 650 F. while silica or quartz fibers will withstand substantially higher temperatures.

The impregnation of the base coating with the lubricious metal sulfide or a metal compound susceptible to conversion to the corresponding metal sulfide, may also be accomplished by simple and conventional methods such as immersion, spraying, etc.

While ammonia fumes are preferably employed to convert the metal salt :to the metal hydroxide or hydrous metal oxide which is ultimately transformed to the corresponding metal oxide, a variety of reactants may be used for this purpose. While compounds capable of yielding the hydroxyl ion or the -OH- H O form of the metal composition are generally suitable, those ionic substances known as alkalies and including ammonium hydroxide as well as the hydroxides of lithium, sodium, potassium, cal cium, strontium, barium and magnesium are particularly useful. It should be noted that the limited solubility of some of the foregoing alkalies renders them of marginal suitability but the deposition of by-products resulting from their use, e.g. barium sulfate, is not particularly detrimental.

When as in the preferred practice, the base coating is impregnated with a metal compound which is subsequently converted to the corresponding metal sulfide, the conversion may be attained by mere exposure to, or immersion in, a sulfur yielding reactant such as hydrogen sulfide gas, a solution of thioacetamide, etc. This exposure is preferably carried out while the previously applied convertible compound is in a wet condition. Subsequent to conversion to the metal sulfide, the coated substrate may be merely air dried.

While chromic oxide is preferred asthe porous base cised in choosing the specific salt of the metal to be utilized since not all of the salts of the same metal yield equivalent results. For example, in the case of chromic oxide base coatings, the sulfate appears to yield a coating which is superior to those formed from the nitrate, chloride or acetate of chromium. In addition, the base coating may comprise a combination of metal oxides, e.g. chromic oxide and aluminum oxide.

While an admixture of barium and silver sulfides in a weight ratio of from 5-5021, and formed in situ from barium and silver salts capable of yielding the sulfide of these metals, is preferred, the sulfide of either of these metals may be employed alone or the sulfides of other metals capable of imparting lubricity and resistant to elevated temperatures may also be employed alone or in admixture. For example, lead sulfide may be formed in situ by exposing a substrate possessing a base metal oxide coating impregnated with lead nitrate to hydrogen sulfide gas. The sulfides of cadmium, lithium, zinc, etc., may be formed in situ by the same or highly similar techniques.

In respect to the preferred admixture of barium and silver nitrates, which are converted in situ to the corresponding sulfides, a 30:1 ratio of the barium and silver salts is desirable and the admixture is preferably applied as a relatively dilute solution, e.g. less than 20. The application of the foregoing system is then calculated to fully permeate the porous base coating although a continuous, external coating of the system, in excess of that required for full penetration, may be utilized. For example, invthe treatment of a fibrous glass fabric of conventional weave, it has been determined thatapproximately 16 grams of chromic sulfate per square yard is adequate for the formation of the base coating, while the subsequent permeation of such a base coating with the lubricious metal impregnant maybe achieved with approximately 6 grams per square yard of the described admixture of barium and silver nitrate.

It should be noted that the lubricious impregnants or a combination thereof, may be combined with other lubricious compounds such as metal oxides, e.g. magnesium oxide; metal carbonates, e.g. lithium carbonate; metal hydroxides, e.g. barium hydroxide, etc.

While hydrogen sulfide gas is preferred for the conversion of the metal salts to the corresponding metal sulfide, other sulfur yielding reactants such as thioacetamide, etc., may also be utilized.

When the treating materials of the present invention are prone to release acidic materials which may leach or weaken the siliceous substrate, e.g. the aqueous metal salt solutions, pH adjustment may be resorted to. For example, a chromic sulfate solution may be acidified with a 5% solution of sulfuric acid and then neutralized with ammonium hydroxide to yield a pH of no less than 4. Such precautions are advisable when treated substrates such as fabrics are to be employed in applications involving flexing since the effect of leached or weakened fibers during the creasing or flexing of such fabrics may result coating, other metal oxides such as zirconia, alumina,

titania, cobaltous oxide, ferric oxide and the like, are also suitable. In effect, the selection of the metal employed as the base coating is only limited by the temperature resistance desired, and by theavailability of appropriate in the breaking of the fibers. However, when static conditions are contemplated, or a weakened substrate is acceptable, incidental acidity and attendant leaching may yield an ancillary benefit in increasing the mechanical bonding of the coatings with the leached or roughened surface of the substrate.

In order to determine the physical characteristics and chemical identity of the inventive coatings, X-raydiffraction analyses and light and electron photomicrogra-phic studies were made. These studies were performed upon fibrous glass fabric which had been coated with chromic sulfate, exposed to ammonia fumes, heated for 12 hours at 600 F., immersed in a barium nitrate-silver nitrate solution and exposed to hydrogen sulfide fumes.

Upon the basis of these studiesit was theorized that the reactions and products set forth in the following chart, are realized:

I. II- III- IV. V.

Application of Exposure to heated. to 600 Impregnation with barium Exposure to H 5 chronic sulfate ammonia Mes and. silver nitrate partially neutralized with amonium hydroxide i A Cr (so a: Cr (80 nli 0- 01 (SO Ht 0 (rehydrates upon 1 2 1,; 3 2 2 t 3 2 2 l; 3 2 cooling) (residual) cr (so H1 0 F us as so mcrso -nno----+Bait0 aSO -)BaS0 $00103 nnzo 3- 1J2 2 3 2 whic ---i rmnlo i Ba no Ag no (residual) -1- 3 8 5 Ba(il0;) (residual) 012,03 DH O-- Cr203 08 0 As 3 2 (crystalline) E s Cro nllO CrO 'uHO--- Cro -nB o- 3 3 rp w) o o-s t), mo rt oo m sse s 0 (HHQ SO (irs p sp (volatiles) It should be noted that the reactions depicted in the above chart were derived from both visual and X-ray diffraction data. For example, the effects of the exposure to the hydrogen sulfide gas could not be positively determined. However, photosensitivity which is an attribute of both barium and silver nitrate, was found to exist. In addition, election photomicrographs revealed the appearance of a new phase consisting of finely disseminated crystalline material upon the surface of the coating, following exposure to the hydrogen sulfide gas.

Electron photomicrographs of the chromic oxide base coating revealed the previously mentioned weathered slate appearance with some indications of particulate agglomeration. Similar studies after application of the barium-nitrate salt solution disclosed an angular surface appearance indicative of a crystalline coating, and as previously mentioned, the sulfide treatment produced fine, discrete particles upon the former angular surface.

It should be noted that the presence of residual materials is for the most part assumed. It must also be realized that the foregoing reactions are in part theoretical and not offered as conclusive evidence, but merely as an attempt to explain the nature of the coatings achieved, and the basis for the improved properties which are realized.

It is also believed, although not conclusively established, that the following reactions and conversions are experienced during high temperature utilizations of the coated products of the invention:

A preferred product and method are set forth by the following example:

Example 1 A heat cleaned fibrous'glass fabric was immersed in a 10% aqueous solution of chromic sulfate until fully saturated. The wet fabric was then exposed to the fumes of a 28% ammonia solution in a closed chamber for a period of 30 seconds, air dried, and then placed in an oven heated to 600 F. for a period of one hour. The specified temperature was selected since the glass fibers were formed from a glass (E glass) which becomes brittle at temperatures in excess of 650 F. While only a partial conversion of the hydrous chromic oxide to chromic oxide was achieved, this degree of conversion proved adequate. However, full conversion may be accomplished at temperatures in the range of 850 F. when silica fibers or fibers formed from glass compositions capable of resisting such a temperature, are subjected to the treatment.

The fabric was then cooled to room temperature and immersed in a 4.4% aqueous solution of 450 parts by weight of barium nitrate and 15 parts by weight of silver nitrate, until saturated. While still wet the fabric was exposed to hydrogen sulfide gas for a period of two minutes and air dried.

In order to demonstrate the efiicacy of materials treated in accordance with the invention, in applications involving heat, dynamic abrasion and flexing, a fabric treated Compositions Present on the Surface A B C of the Substrate (In Probable Order of Decreasing Magnitude) In Use at 500 F. In Use at 600 F. In Use at 825 F.

GlzOa-IlHgO CI'zOQ-DH O-i-HQO T CI'Og-CXzOg-i-HgO T grz gol 411120 O12(SO4)3-BH2O+H2O l Crz(SO4)a-DH1O+HO T- gngm); (anhydrous) a 4 a 4 NH NO3 NH; t +NO; I +H2OT Ht)a (S 4)a 4)a 4): AgNO; Molten AgNOa Ag O BaNOs B8(NO3)1 AgzS AggS BaS; BaSa 9 as described in Example 1 was compared with fabrics treated with two different silicone compositions which are conventionally employed in high temperature applications. The performance of these fabrics under conditions of high temperature and flex inspired abrasion is illustrated by Table 1 below:

TABLE 1 Temperature Number of Fabric Treatment (Degrees Revolutions Fahrenheit) Prior to Breaking Silicone A 500 180, 000 500 738,000 Example 1 500 900, 000

Silicone A 550 90, 000 Silicone B. 550 540. 000 Example 1 550 840, 000

Silicone A"... 000 40, 000 Silicone B 600 485, 000 Example 1 600 650,000

Silicone A 650 20, 000 Silicone B 650 200, 000 Example 1 650 635, 000

It must be observed that under all of the above conditions of temperature, the inventive fabric was enabled to withstand between 162,000 to 435,000 revolutions more than the next best candidate, to yield a 22% to 218% improvement in resistance to flexing at temperatures in the range of 5 -65 0 F. In addition, the inventive fabric retained 70% of its abrasion or flexural resistance during a temperature increase from 500 to 650 F. while the two silicone treated fabrics only retained 11% and 27% under the same conditions.

All of the fabrics treated to provide the data set forth in Table 1 were heat cleaned prior to treatment at 650 F. for 24 hours.

Illustrations of other suitable treatments are provided by the following examples:

Example 2 A fibrous glass fabric was immersed in a 10% solution of chromic sulfate until saturated, exposed to ammonium hydroxide vapors for a period of 30 seconds and heated at 650 F. for one hour. The fabric was then immersed in a 6 aqueous solution of one part by weight of lithium chloride and parts by weight of barium chloride until saturated, subjected to a second immersion in a 8% aqueous solution of thioacetamide and air dried.

Example 3 Example 2 was repeated with the substitution of a 6% solution of equal parts by weight of silver chloride and cadmium chloride for the solution of lithium and barium chloride which was employed in Example 2.

Example 4 Example 2 was repeated with the substitution of a 6% solution of 5 parts by weight of cadmium chloride and 1 part by weight of lithium chloride, for the lithium and barium chloride solution which was employed in Example 2.

Example 5 Example 2 was repeated with the substitution of a 10% solution of lithium chloride for the lithium and barium chloride solution which was utilized in Example 2.

Example 6 A fabric coated only with the porous chromic oxide base coating was prepared by immersing the fabric in a 10 10% solution of chromic sulfate until saturated, exposing it to ammonium hydroxide vapors for a period of 30 seconds and heating it at 650 F. for one hour. No lubricious impregnant was applied.

The desirability of the combination of a porous metallic oxide base coating and a lubricious metallic sulfide impregnating coating, and the efiicacy of a variety of single and combined lubricious impregnants, is demon- I strated by the data embodied in Table 2 below:

TABLE 2 Number of Base Coating Lubricious Impregnant Example Flexing Number Revolutions Silicone Resin None 45,000 Chromic Oxide Lithium and Barium 2 5, 208, 000

Sulfides. Silver and Cadmium 3 1, 608, 000

sulfides. Cadmium and Lithium 4 585, 000

sulfides. Lithium Sulfide 5 570,000 None 6 240, 000

To further demonstrate the desirability and function of the metal oxide base coating two fabrics were immersed until saturated in a 10% aqueous solution of chromic sulfate, exposed to ammonium hydroxide vapors for a period of 30 seconds, heated at 500 F. for a period of one hour, immersed in an 8% aqueous solution of 2 parts by weight of silver chloride and 6 parts by weight of barium chloride until saturated, subsequently immersed in a solution of thioacetamide, and air dried. However, in the case of one fabric, the saturation by the chromic sulfate was followed by blotting with an absorbent material, to remove a portion of the chromic sulfate solution. The result of the diminution of the base coating, without a corresponding change in the lubricious secondary impregnant, is illustrated by the data embodied in Table 3, below:

TABLE 3 Sample Number of Flexing Revolutions (500 F.)

A. Chromic oxide base coating impregnated with silver and barium sulfides 570, 000 B. Same as A with reduction in quantity of chromic oxide base coating 105,000

It should be noted that the fabric employed for both sample A and sample B in Table 3, was subjected to a severe heat treatment, i.e. 6 8 hours at 650 F., prior to subjection to the treatment of Example 7.

On the basis of the data provided by Tables 2 and 3, it may be readily perceived that the improvements of the invention are the cumulative effect of: (a) the existence of a porous metal oxide base coating, and (b) the impregnation of such a base coating with a lubricious metal compound. Specifically, Table 2 demonstrates that the porous metal oxide base coating alone, is incapable of yielding the inventive improvement, and such improvement is achieved only when the base coating is subsequently impregnated with a lubricious metal compound. In addition, Table 3 illustrate the fact that the lubricious secondary impregnant is also incapable of yielding the inventive improvement when an adequate base coating is absent, e.g. through removal by blotting. Consequently, it is apparent that the combination of the base coating and the secondary, lubricious impregnant is essential for the realization of the full contribution of the invention.

It has also been found that the heat treatment of the base coating, and at least a partial conversion to the corresponding metal oxide, is productive of improved results as demonstrated by Example 8 and Table 4, below:

Example 8 TAB LE 4 Number of Sample Heat Treatment Flexing Revolutions (600 F.)

A. Chromic oxide base coating and None 795, 000

lithium sulfide impregnant. B. Chromic oxide base coating and 2 hours at 650 F 3, 135, 000

lithium sulfide impregnant.

While the foregoing description has been principally concerned with the treatment of fabrics or the like which have previously been formed from siliceous fiber strands, it should be noted that the methods and materials of the invention are suitable for application to such siliceous fibers during their formation. For example, the forming and coating methods and apparatus disclosed in US. 2,390,370; 2,846,348 and 2,732,883 with one or more applicators utilized to apply the coating materials, and in combination with appropriate heating and impregnating apparatus positioned in line and between the fiber forming and winding equipment, may be utilized in the practice of the invention.

In addition, while the invention has been principally discussed in respect to glass fibers it should be noted that other siliceous fibers are also enhanced by the inventive treatments. For example, mineral wool and silica fibers derived by the acidic leaching of conventional glass fibers or through the attenuation of quartz rods are greatly improved by the invention since silica fibers are more highly susceptible to the harmful effects of mutual abrasion. In such substrates improved thermal resistance is also of value since their principal use is in high temperature applications. For example, the ablation resistance of reinforced plastics reinforced with silica fibers treated in accordance with the invention has been found to be greatly improved. In addition, combinations of siliceous fibers with other fibers, e.g. organic fibers which are partially heat resistant or even destroyed during a thermal phase, are also susceptible to the practices of the invention. Further-more, thermally inert substances such as colloidal silica, alumina, titania, zirconia, etc., may also be incorporated in either the base coating composition or in the subsequent impregnant.

It is apparent that novel, treated siliceous substrates characterized by greatly improved thermal and abrasion resistance, as well as methods for the preparation of such substrates, are provided by the present invention.

It is also obvious that various changes, alterations and substitutions may be made in the materials, methods and products of the invention without departing from the spirit of the invention as defined by the following claims.

I claim:

1. In a method for the preparation of high temperature and abrasion resistant glass fibers, the sequential steps of applying from 5 to 25% by weight of an aqueous solution of a metal salt to the surfaces of said fibers, converting said salt to the corresponding metal oxide in situ, to form a base coating,

applying an aqueous solution of metal salt to said base coating, and then,

converting said metal salt in situ to the sulfide by reaction with a compound capable of yielding the sulfide ion selected from the group consisting of sulfur, hydrogen sulfide and thioacetamide, to form a lubricious metal sulfide coating on said base coating.

2. A method as claimed in claim 1 in which said base coating is selected from the group consisting of the oxides of chromium, aluminum, zirconium, titanium, cobalt and iron.

3. A method as claimed in claim 1 in which said base coating is chromic oxide.

4. A method as claimed in claim 1 in which said lubricious metal sulfide coating is one from the group consisting of the sulfides of barium, silver, cadmium, lithium, lead and zinc and combinations of these in a dilute aqueous solution of from l20%.

5. A method as claimed in claim 1 in which said lubricious metal sulfide coating is an admixture of between 550 parts by weight of barium sulfide and one part by weight silver sulfide.

6. A method for the preparation of siliceous fibers resistant to high temperature and abrasion, comprising applying to the surfaces of said siliceous fibers between 5 to 25% by weight of chromic sulfate, exposing said chromic sulfate to an alkali to form hydrous chromic oxide, exposing said hydrous chromic oxide to temperatures adequate to convert at least a portion of said hydrous chromic oxide to chromic oxide, impregnating said chromic oxide with an admixture of between 5 to 50 parts by weight of barium nitrate and one part by weight of silver nitrate, and exposing the impregnated chromic oxide to a compound capable of yielding the sulfide ion selected from the group consisting of sulfur, hydrogen sulfide, and thioacetamide.

7. In a method for the preparation of glass fibers resistant to high temperature and abrasion, the steps comprising applying between 5-25% by weight of a water soluble metal salt to the surfaces of said fibers,

converting said salt to the hydroxide by exposure to an alkali,

heating said metal hydroxide to of metal oxide,

impregnating said porous coating with a second water soluble metal salt,

converting said salt to the metal sulfide, in situ, by

reaction with a compound capable of yielding the sulfide ion selected from the group consisting of sulfur, hydrogen sulfide, and thioacetamide thereby forming a lubricious coating, which when worn away, is replenished from its reservoir in the porous metal form a porous coating 13 14 oxide base coating to form a continuous coating References Cited through friction. 8. In a method for the preparation of glass fibers as UNITED STATES PATENTS claimed in claim 7, wherein the compound capable of 2,901,379 4/1956 Shannon et aL 117126 X yielding the sulfide ion is hydrogen sulfide. 5 3,075,279 1/1963 Haltner et 117'16'9 X 19;. In; a method ifor 116 pregaration of gliass fi bglrs a; FOREIGN PATENTS came in calm w erein e compoun capa e 0 562,080 8/1958 Canada yielding the sulfide ion is thioacetamide.

10. In a method for the preparation of glass fibers as claimed in claim 7, wherein the compound capable 10 ALFRED LEAVITT P'lmary Exammer of yielding the sulfide ion is sulfur. H. COHEN, Assistant Examiner. 

